1. Field of the Invention
The present invention relates to an optically coupled device and an optical module including the optically coupled device. In particular, the present invention relates to an optically coupled device and an optical module including the optically coupled device suitable for optically coupling a photoelectric conversion device and a multi-mode optical fiber.
2. Description of the Related Art
In recent years, with increasing speed and capacity of data communication, the need is further rising for an optical fiber communication technology using an optical fiber.
An optical fiber communication technology such as this uses an optically coupled device to which an optical fiber and a photoelectric conversion device (such as a semiconductor laser or a photodetector) are attached. In many optically coupled devices, a surface facing a photoelectric conversion element (light-emitting unit or light-receiving unit) of the photoelectric conversion device and a surface facing an end surface of the optical fiber are formed into lens surfaces.
In this type of optically coupled device, for example, light emitted from a semiconductor laser is coupled to the end surface of the optical fiber using transmittance and refraction of light by the lens surfaces.
Among optically coupled devices, some include a lens array structure in which a plurality of lens surfaces are arranged to correspond to a plurality of optical fibers (multi-core optical fiber and the like)
FIG. 8 is a front view of an example of a conventional optically coupled device 1 having a lens array structure such as this. FIG. 9 is a planar view of FIG. 8. FIG. 10 is a right side view of FIG. 8.
In the optically coupled device 1 in FIG. 8, a photoelectric conversion device can be attached from the front to a front end surface (front end surface in FIG. 8) 2. A plurality of optical fibers can be attached from above to a front end surface 3. A plurality of photoelectric conversion elements that emit or receive light are formed in an array along a lateral direction in FIG. 8. The optical fibers are arrayed in the lateral direction in FIG. 8. A substrate-mounted photoelectric conversion device functioning as at least one of a vertical cavity surface emitting laser (VCSEL) and a photodetector, for example, is attached as the photoelectric conversion device. The plurality of optical fibers are housed within a connector and attached with the connector.
As shown in FIG. 8, on the front end surface 2 of the optically coupled device 1, a plurality of first lens surfaces 5 are formed on a surface portion 2a in an array, such as to be adjacent to one another along the lateral direction. The first lens surfaces 5 are convex towards the front (the front side in FIG. 8). The surface portion 2a is formed in a center portion and has a planar, roughly rectangular shape that is long in the lateral direction. The first lens surfaces 5 can form optical paths connecting each photoelectric conversion element of the photoelectric conversion device and each end surface of the optical fibers.
As shown in FIG. 8, on the front end surface 2 of the optically coupled device, an outer side surface portion 2b of the surface portion 2a on which the first lens surfaces 5 are formed is formed parallel to the surface portion 2a and higher towards the photoelectric conversion device side (front) in a surface normal direction of the surface portion 2a in relation to the surface portion 2a. When the photoelectric conversion device is attached to the optically coupled device 1, a semiconductor substrate of the photoelectric conversion device comes into contact with the outer side surface portion 2b. 
Moreover, as shown in FIG. 8, a pair of circular positioning holes 7 is formed on positions near both outer sides of the surface portion 2a on which the first lens surfaces 5 are formed, in a direction in which the first lens surfaces 5 are arrayed. The positioning holes 7 are used for positioning the photoelectric conversion device when the photoelectric conversion device is attached to the optically coupled device 1. Specifically, when the photoelectric conversion device is attached, a pair of positioning pins (not shown) passing through the substrate of the photoelectric conversion device respectively engage with each positioning hole 7, thereby positioning the photoelectric conversion device.
On the other hand, as shown in FIG. 9, on a top end surface 3 of the optically coupled device 1, a plurality of second lens surfaces 8 are formed on a surface portion 3a in an array, such as to be adjacent to one another along the lateral direction. The second lens surfaces 8 are convex towards the front side in FIG. 9 (upward in FIG. 8). The surface portion 3a is formed in a center portion and has a planar, roughly rectangular shape that is long in the lateral direction. Each second lens surface 8 forms a pair with a first lens surface 5. With the first lens surfaces 5, the second lens surfaces 8 can form optical paths connecting each of the photoelectric conversion elements of the photoelectric conversion device and each end surface of the optical fibers. A distance between center points of the second lens surfaces 8 that are adjacent to each other is formed to match a distance between the center points of the first lens surfaces 5 that are adjacent to each other.
As shown in FIG. 9, on the upper end surface 3 of the optically coupled device, an outer side surface portion 3b of the surface portion 3a on which the second lens surfaces 8 are formed is formed parallel to the surface portion 3a and higher towards the optical fiber side (front side in FIG. 9 and upwards in FIG. 8) in a surface normal direction of the surface portion 3a in relation to the surface portion 3a. When the optical fibers are attached to the optically coupled device 1, the connector of the optical fibers comes into contact with the outer side surface portion 3b. 
Moreover, as shown in FIG. 9, a pair of columnar positioning pins 10 is formed on positions near both outer sides of the surface portion 3a on which the second lens surfaces 8 are formed, in a direction in which the second lens surfaces 8 are arrayed. The positioning pins 10 are used for positioning the optical fibers when the optical fibers are attached to the optically coupled device 1. Specifically, when the optical fibers are attached, the positioning pins 10 engage with a pair of positioning holes (not shown) formed on the connector of the optical fibers, thereby positioning the optical fibers.
As shown in FIG. 10, a reflection surface 12 is formed on a rear end surface 11 of the optically coupled device 1 in a recessing manner. The reflection surface 12 is at an angle of about 45° to both an optical axis OA1 of the first lens surfaces 5 and an optical axis OA2 of the second lens surfaces 8. The reflection surface 12 can switch between an optical path of light traveling on the optical axis OA1 of the first lens surfaces 5 and an optical path of light traveling on the optical axis OA2 of the second lens surfaces 8, through reflection of the light. Therefore, the reflection surface 12, with the plurality of first lens surfaces 5 and the plurality of second lens surfaces 8, can form optical paths connecting each of the plurality of photoelectric conversion elements of the photoelectric conversion device and each end surface of the plurality of optical fibers.
In an optically coupled device 1 such as this, the optical fibers can be pulled out in parallel with the semiconductor substrate of the photoelectric conversion device. Therefore, the optically coupled device 1 has an advantage of requiring less physical space.
In an optically coupled device 1 such as this, to allow the first lens surfaces 5 and the second lens surfaces 8 to form a desired optical path, it is important that each lens surface 5 and 8 is formed with significant precision at a targeted position.
However, depending on manufacturing conditions, such as dimensional accuracy of a mold used to form the optically coupled device, positional accuracy of each lens surface 5 and 8 may not be sufficiently achieved, initially.
Therefore, conventionally, when the optically coupled device 1 is manufactured, at a product inspection stage, the position of each lens surface 5 and 8 in a product is measured. Based on measurement results, manufacturing conditions, such as adjustment of the mold, are adjusted accordingly, thereby ensuring the positional accuracy of the lens surfaces 5 and 8.
In a positional measurement of the lens surfaces, such as this, aiming to ensure the positioning accuracy of the lens surfaces, various measurement methods can be considered, such as a contact-type measurement method in which the lens surfaces are stroked by a probe, and a non-contact-type optical measurement method in using a tool microscope and an image measurement device. However, in terms of performing the positional measurement without damaging the lens surfaces that have small dimensions, the optical measurement method is preferred.
An example of an optical lens surface position measurement method is as follows. First, as shown in FIG. 11A, the optically coupled device 1 is set on the tool microscope in a state allowing the planar shape of the first lens surfaces 5 to be visible. At this time, the second lens surfaces 8 are not visible.
Then, after an outline of the upper end surface 3 extending in the lateral direction in FIG. 11A is recognized, two points, P1 and P2, that are separated from each other are taken on the outline. A line connecting the two points P1 and P2 is assumed. The line is defined as a Y axis of an XY coordinate system (two-dimensional Cartesian coordinate system).
Next, respective center lines L1 and L2of the two positioning pins 10 are determined. A line at an equal distance from the two center lines L1 and L2 and parallel to both center lines L1 and L2 is determined. The line is defined as an X axis of the XY coordinate system.
Then, after an intersection between the X axis and the Y axis is determined to be a point of origin (0,0) in the XY coordinate system, the position measurement of the first lens surfaces 5 is performed by the X coordinate and the Y coordinate of a center point of each first lens surface 5 being determined.
Next, as shown in FIG. 11B, the optically coupled device 1 is set on the tool microscope in a state allowing the planar shape of the second lens surfaces 8 to be visible. At this time, the first lens surfaces 5 are not visible.
Then, after an outline of a portion (lower side edge in FIG. 11B) of the upper end surface 3 extending in the lateral direction in FIG. 11B is recognized, two points, P1′ and P2′, that are separated from each other are taken on the outline. A line connecting the two points P1′ and P2′ is assumed. The line is defined as a Y axis of an XY coordinate system.
Next, respective center points S1 and S2 of the two positioning pins 10 are determined. Center lines L1′ and L2′ passing through the two center points S1 and S2 and perpendicular to the Y axis are determined. A line at an equal distance from the two center lines L1′ and L2′ and parallel to both center lines L1′ and L2′ is determined. The line is defined as an X axis of the XY coordinate system.
Then, after an intersection between the X axis and the Y axis is determined to be a point of origin (0,0) in the XY coordinate system, the position measurement of the second lens surfaces 8 is performed by the X coordinate and the Y coordinate of a center point of each second lens surface 8 being determined.
In this way, conventionally, the position measurement of the lens surfaces 5 and 8 using the tool microscope is performed by an XY coordinate system being defined, with a predetermined area (such as the positioning pins 10) of the optically coupled device 1 as a reference.
Patent Literature 1: Japanese Patent Laid-open Publication No. 2005-31556
In the above-described optically coupled device 1, to allow an arbitrary first lens surface 5 and a corresponding second lens surface 8 to appropriately form an optical path, the Y coordinates of the center points of both lens surfaces 5 and 8 are required to match.
On the other hand, conventionally, during position measurement of the first lens surface 5, the XY coordinate system is defined based on a side surface shape of the positioning pins 10. During position measurement of the second lens surface 8, the XY coordinate system is defined based on a planar shape of the positioning pins 10. Therefore, even when the same positioning pins 10 serve as the reference for the XY coordinate system, depending on the dimensional accuracy of the positioning pins 10, high-precision position measurement of ht lens surfaces 5 and 8 is impeded.
In other words, when the positioning pins 10 are formed having an accurate columnar shape, the center lines L1 and L2 of the side surface shape of the positioning pins 10 shown in FIG. 11A passes through the center points S1 and S2 of the planar shape of the positioning pins 10 shown in FIG. 11B. In this case, shifting in the Y-axis direction does not occur between the center lines L1 and L2 in FIG. 11A and the lines L1′ and L2′ passing through the center points S1 and S2 in FIG. 11B. The Y coordinate of the point of origin in the XY coordinate system defined in FIG. 11A and the Y coordinate of the point of origin in the XY coordinate system defined in FIG. 11B match. In this case, when the Y coordinate of an arbitrary first lens surface 5 measured using the XY coordinate system defined in FIG. 11A matches the Y coordinate of the second lens surface 8 corresponding to the arbitrary first lens surface 5 measured using the XY coordinate system defined in FIG. 11B, the positions of both lens surfaces 5 and 8 can be judged to be appropriate.
However, when the positioning pins 10 are not formed having an accurate columnar shape, the center lines L1 and L2 in FIG. 11A do not pass through the center points S1 and S2 in FIG. 11B. In this case, misalignment in the Y-axis direction occurs between the center lines L1 and L2 in FIG. 11A and the lines L1′ and L2′ passing through the center points S1 and S2 in FIG. 11B. The Y coordinate of the point of origin in the XY coordinate system defined in FIG. 11A and the Y coordinate of the point of origin in the XY coordinate system defined in FIG. 11B do not match. In this case, when the positions of both lens surfaces 5 and 8 are judged to be appropriate because the Y coordinate of an arbitrary first lens surface 5 measured using the XY coordinate system defined in FIG. 11A matches the Y coordinate of the second lens surface 8 corresponding to the arbitrary first lens surface 5 measured using the XY coordinate system defined in FIG. 11B, an erroneous judgment is made.
Moreover, conventionally, the XY coordinate system used for the position measurement of the first lens surfaces 5 and the XY coordinate system used for the position measurement of the second lens surfaces 8 are required to be separately defined by a same procedure. Therefore, the position measurement of the lens surfaces cannot be efficiently performed.
In other words, conventionally, a problem occurs in that an appropriate and efficient position measurement of the lens surfaces is difficult to perform.